The photodynamic therapy(PDT), according to which photosensitizers having a specific affinity for tumor cells are administered to patients before irradiation by laser beams of various wavelengths for treatment of tumors, is now attracting attention as a non-invasive therapy for cancers. PDT enables to exhibit an ability of damaging or killing the tumor cells by excitation of photosensitizers collected to tumor cells at low doses of light irradiation, thus to protect adjacent normal cells from damaging, and to eradicate locally only tumor cells. Known photosensitizers usable for PDT include various derivatives having a porphyrin skeleton or fullerene skeleton, some of which are used clinically.
Desirable photosensitizers usable for PDT are required to be hydrophilic and highly selective to tumor cells and harmless to cells in a dark place. The fullerene derivatives proposed in Japanese Unexamined Patent Publication No. Hei 9-235235 are aimed at directing a target to cancer tissues by enhancing water solubility after modifying fullerene chemically with a water-soluble polymer, polyethylene glycol(PEG). It has been reported that accumulation of a fullerene-PEG combination in cancerous tissues is high when compared with that in normal tissues and that in photodynamic therapy experiments for cancers, masses have disappeared under light irradiation. Since fullerene is chemically modified with PEG, the results concerning enhancement of organic selectivity such as an affinity to cell walls of various organs have not been reported.
Also, Japanese Unexamined Publication No. Hei 11-255794 discloses fullerene derivatives of which fullerene was modified by sugar residues having a protected hydroxyl group. However, the publication does not describe the water solubility of the derivatives and target directivity to cancerous tissues.